These are examples of White playing too close to strong black formations. No good will come of this: White will be short of liberties quickly, while having not much effect on Black.
There are more appropriate ways to help out or use the stones.
These plays by White are lighter and rather better: in the case of White takes a relaxed view of Black a, being prepared to sacrifice the initial stone.
A basic guideline is only to play for some definite effect. It isn't necessarily being particularly aggressive to fill in liberties on a group of the opponent's. That is one motivation for playing close, but it is mostly unskilful and leads to cutting points and shortage of liberties.
See also